These studies are designed to further evaluate in intact unanesthetized dogs the relationship between early measurements of ischemic blood flow and subsequent myocardial infarction and the direct effects of acutely injured myocardium on tissue perfusion. Studies will be performed using models of acute infarction produced by permanent and transient coronary occlusion. Using the close relationship between regional blood flow and infarcted myocardium, studies will be outlined to test interventions which alter the extent of myocardial injury and to determine whether the local alterations in tissue perfusion are responses to reversible cellular injury. BIBLIOGRAPHIC REFERENCES: Roe, C.R., Cobb, F.R., and Starmer, F.C.: The relationship between enzymatic estimates and histologic extent of myocardial infarction. Circulation 55:438-449, 1977. Irvin, R., and Cobb, F.R.: Relationship between epicardial ST segments and regional blood flow measurements and extent of acute myocardial infarction. Circulation 55:825, 1977.